This is not uncommon with many vehicles, particularly in winter. Just like walking from the cold, dry outside air into a carpeted home, then touching a metal doorknob or handrail -- ZAP! -- a static electrical shock.
Years ago, parts stores sold plastic-coated ground straps that would be bolted to the rear bumper to drag on the pavement and provide a ground path for this static electricity. I actually saw a late-model GM truck with a pair of these hanging from the rear bumper just last week. But I don't know where they're available these days.
I have also seen some data indicating that the reduction in the use of carbon black in the manufacturing of tires might contribute to a static electricity problem. But more recently, a caller to my Detroit radio show confirmed that upholstery fabrics cause static buildup. He should know; he worked for one of the auto industry's large interior suppliers.
So it appears that an aerosol anti-static product is the right answer. Perhaps even tossing a couple of anti-static cloths on the seat might help.
But here's the more immediate answer. When exiting the vehicle, make contact with a metal part of the body before stepping onto the ground or pavement. This won't prevent the static charge, but it will ground it through your shoe rather than your fingers.